Development of novel glass-based composite seals for planar intermediate temperature solid oxide fuel cells

Novel glass-based composite seals prepared by tape casting are evaluated as sealing materials in solid oxide fuel cell. The leakage rates are measured at the inlet pressure of 1, 2 and 3 psi under different compressive stresses and temperatures respectively. The results show that all of measured leakage rates are lower than 0.01 sccm cm⁻¹ and increase with higher inlet pressure and lower test temperatures. The leakage rates during thermal cycling are conducted under a compressive stress of 20 psi at 750 °C, which indicate excellent thermal cycle stability of the seals. Good compatibility between seals and the adjacent components provide well interface contact which could avoid the formation of leakage paths. When the seal is applied for single cell testing, the open circuit voltage of 1.13 V and undetectable degradation clearly demonstrate the applicable performance of glass-based composite seal in solid oxide fuel cell.     

Thermal cycle stability of Al2O3-based compressive seals for planar intermediate temperature solid oxide fuel cells

Al₂O₃-based compressive seals were fabricated by tape casting with Al₂O₃ and 0-30 wt% aluminum powders, and their sealing effectiveness, thermal cycle stability between 200 and 750 °C and applicability in planar intermediate temperature solid oxide fuel cells were evaluated. The results indicate that increasing the aluminum content from 0 to 30 wt% in the seals decreases the leakage rate and increases the thermal cycle stability under various inlet gas (N₂) pressures of 3.5, 7.0 and 10.5 kPa. Especially, with the seal containing 30 wt% of aluminum (ACS3), the initial leakage rate was below 0.03 sccm cm⁻¹ under an inlet pressure of 10.5 kPa, and the leakage rates during 96 thermal cycles were below 0.04 sccm cm⁻¹ under the same inlet gas pressure. The interfaces in the interconnect/seal/cell assembly with the ACS3 seal retained integrity after 50 thermal cycles, demonstrating the applicability of the Al₂O₃-based compressive seals in the planar intermediate temperature SOFCs.     

Electrochemical performance assessment of low-temperature solid oxide fuel cell with YSZ-based and SDC-based electrolytes

In this work, solid oxide fuel cells (SOFCs) based on different electrolytes, i.e., the yttria-stabilized zirconia (YSZ) and the samaria-doped ceria (SDC), were investigated to study their performances at low-temperature operation. The predicted performance of both SOFCs was validated with the experimental results. The verified models were implemented to study the impact of operating conditions, i.e., cell temperature, pressure, thicknesses of cathode, anode, and electrolyte, on their performances. The decrease in the operating temperature from intermediate range (800–900 °C) to low range (550–650 °C) has a considerable effect on the performance of the YSZ-based SOFC as conventional type, which dropped from 0.67–1.40 W/cm² to 0.027–0.13 W/cm². Under the low operating temperature range, the performance of SDC-based SOFC was superior to that of the YSZ-based SOFC, due to the lower ohmic loss. Nevertheless, the SDC-based SOFC has higher concentration overpotentials than the YSZ-based SOFC. The concentration overpotentials of the SDC-based SOFC can be reduced by the thinner anode and cathode thicknesses. In addition, the SDC-based SOFC at low operating temperature with the pressurized operation could significantly improve its power density, about 20% at 2 bar, which was close to that of YSZ-based SOFC at intermediate temperature of 800 °C.     

Dual ionic conductive membrane for molten carbonate fuel cell

Within this study, the electrochemically inert, molten carbonate fuel cell (MCFC) $\text{γ}$-LiAlO₂ matrix is replaced by oxygen ion conducting ceramics, typical for solid oxide fuel cell (SOFC) application. Such solution leads to synergistic ion transport both by molten carbonate mix (CO₃^2-) and yttria-stabilized zirconia (YSZ) or samaria-doped ceria (SDC) matrix (O^2-).Single unit cell tests confirm that application of hybrid ionic membrane increases the performance (power density) of the MCFC over pure $\text{γ}$-LiAlO₂ for a wide range of operating temperatures (600 °C–750 °C). Cell power density with SDC and YSZ matrices is 2% and 13% higher, respectively, compared to the $\text{γ}$-LiAlO₂ at typical 650 °C operating temperature of MCFC.     

Porous nickel-iron alloys as anode support for intermediate temperature solid oxide fuel cells: II. Cell performance and stability

Porous nickel–iron alloy supported solid oxide fuel cells (SOFCs) are fabricated through cost-effective ceramic process including tape casting, screen printing and co-sintering. The cell performance is characterized with humidified hydrogen as the fuel and flowing air as the oxidant. Effects of iron content on the cell performance and stability under redox and thermal cycle are investigated from the point of view of structural stability. Single cells supported by nickel and nickel–iron alloy (50 wt % iron) present relatively high discharge performance, and the maximum power density measured at 800 °C is 1.52 and 1.30 W cm^?2 respectively. Nickel supported SOFC shows better thermal stability between 200 and 750 °C due to its dimensional stable substrate under thermal cycles. Posttest analysis shows that a dense iron oxide layer formed on the surface of the nickel-iron alloy during the early stage of oxidation, which prevents the further oxidation of the substrate as well as the functional anode layer, and thus, making nickel-iron supported SOFC exhibits better redox stability at 750 °C. Adding 0.5 wt % magnesium oxide into the nickel-iron alloy (50 wt% iron) can inhibit the metal sintering and reduce the linear shrinkage, making the single cell exhibit promising thermal stability.     

Electricity production from lignocellulosic biomass by direct coupling of a gasifier and a Nickel/Yttria-stabilized Zirconia-based solid oxide fuel cell. Part 1: From gas production to direct electricity production

This work presents the direct coupling of a gasification pilot according to the patented concept by S3D Company and of a Ni-YSZ-based SOFC. The composition of gas issued from the gasifier is rather stable, with H₂ ≈ 15%, CO ≈ 15%, CH₄ ≈ 1%, CO₂ ≈ 20% and N₂ ≈ 49%. Before injecting directly the gas on the cell, a preliminary test of the home-made cell consisting of an industrial Fiaxell Nickel/Yttria-stabilized Zirconia-based anode-electrolyte assembly covered by praseodymium nickelate oxide was performed with H₂N₂ mixtures. The cell is tested at 750 °C and 850 °C, with a maximum power density of 1.4 W cm^?2 at 850 °C when fueled with a 76%–24% H₂Ar mixture. The effect of the dilution of the gas is also studied, and validates the use of a bag containing the gas issued from the gasifier. In these conditions, using exclusively the fuel issued from biomass, without any additional purification steps, maximum power densities of 340 mW cm^?2 and 113 mW cm^?2 can be obtained at 850 °C and 750 °C respectively.     

Electrochemical performance and stability of nano-structured Co/PdO-co-impregnated Y2O3 stabilized ZrO2 cathode for intermediate temperature solid oxide fuel cells

Palladium (Pd) is an attractive cathode catalyst component for solid oxide fuel cells (SOFCs) that has high tendency to agglomerate during operation at around 800 °C. This work shows that such agglomeration can be inhibited by alloying Co into Pd. PdO, Pd_0.95Co_0.05O, Pd_0.90Co_0.10O, and Pd_0.80Co_0.20O were synthesized and characterized. Powder X-ray diffraction patterns at 750 and 900 °C confirmed that PdO decomposition to Pd which normally occurred at 840 °C was suppressed for Co containing Pd alloys while thermal gravimetric analyses indicated improved redox reversibility of PdO ? Pd conversion for alloys during the thermal cycling between 600 and 900 °C. Scanning electron microscopy images supported these arguments. Pd_0.90Co_0.10+yttria stabilized zirconia (YSZ) electrode (i.e., 10 mol % Co containing PdO-impregnated YSZ electrode) displayed the highest oxygen reduction reaction (ORR) performance and stability. The polarization resistance for ORR on Pd_0.90Co_0.10+YSZ cathode is only 0.088 Ω cm² at 750 °C. During polarization test at 750 °C, Pd_0.90Co_0.10+YSZ cathode showed stable performance for 30 h while the performance of Pd+YSZ cathode degraded after 10 h.     

Monolithic flat tubular types of solid oxide fuel cells with integrated electrode and gas channels

A new monolithic solid oxide fuel cell (SOFC) design stacked with flatten tubes of unit cells without using metallic interconnector plate is introduced and evaluated in this study. The anode support is manufactured in a flat tubular shape with fuel channel inside and air gas channel on the cathode surface. This design allows all-ceramic stack to provide flow channels and electrical connection between unit cells without needing metal plates. This structure not only greatly reduces the production cost of SOFC stack, but also fundamentally avoids chromium poisoning originated from a metal plate, thereby improving stack stability. The fuel channel was created in the extrusion process by using the outlet shape of mold. The air channel was created by grinding the surface of pre-sintered support. The anode functional layer and electrolyte were dip-coated on the support. The cathode layer and ceramic interconnector were then spray coated. The maximum power density and total resistance of unit cell with an active area of 30 cm² at 800 °C were 498 mW/cm² and 0.67 Ωcm², respectively. A 5-cell stack was assembled with ceramic components only without metal plates. Its maximum power output at 750 °C was 46 W with degradation rate of 0.69%/kh during severe operation condition for more than 1000 h, proving that such all-ceramic stack is a strong candidate as novel SOFC stack design.     

Novel Al2O3-based compressive seals for IT-SOFC applications

Novel compressive Al₂O₃-based seals were developed and characterized under simulated intermediate temperature solid oxide fuel cell (IT-SOFC) environment. The seals were prepared by tape casting, mainly composed of fine Al₂O₃ powder with various contents of fine Al powder addition. The leakage rates were determined at 800 °C under 0.14–0.69 MPa compressive stresses, and the stabilities were evaluated at 750 °C under constant 0.35 MPa compressive stress. The leakage rates at 800 °C were in range of 0.2–0.01 sccm cm⁻¹, decreasing with increasing the compressive stress and Al content; Al addition significantly improved the stability, the leakage rate with 20 wt% Al addition was as low as 0.025 sccm cm⁻¹ at 800 °C under 0.35 MPa compressive stress with a gauge pressure of 6.9 kPa, and exhibited good stability at 750 °C. Single cell test also confirmed the effectiveness of the tape cast Al₂O₃-based seal for planar IT-SOFC applications.     

Improved electrochemical performance and durability of butane-operating low-temperature solid oxide fuel cell through palladium infiltration

Low-operating-temperature solid oxide fuel cells (LT-SOFCs) with various kinds of fuel, such as hydrocarbons, biogas, natural gas, and oxygenated fuel has been an active SOFC research topic. However, conventional SOFC anodes comprised of nickel metal and yttria-stabilized zirconia composite (Ni-YSZ) experience rapid degradation when operated for the butane direct internal steam reforming (B-DISR), especially at a low temperature (LT) range. This study reveals that the impregnated Pd into the Ni-YSZ anode support of thin-film SOFCs (TF-SOFCs) is effective for achieving better performance and stability regarding the TF-SOFC in B-DISR at 600°C. Adding Pd as a dopant into Ni-YSZ significantly promotes the catalytic activity due to the Pd-Ni alloy formation, both on the YSZ grain and the Ni grain surface. The electrochemical performance of cells without Pd (Ni-YSZ cell) and a Pd-infiltrated Ni-YSZ anode (Pd-Ni-YSZ cell) are compared at 600°C for the B-DISR mode at a ratio of steam-to-carbon of 3. Finally, long-term durability tests were performed at 600°C and under 0.15 A cm⁻². The Pd infiltration decreases the deterioration rate to 0.63 mV h⁻¹ after the first 80 hours of operation for the Pd-Ni-YSZ cell, which was a significant improvement from that of the Ni-YSZ cell, 3.75 mV h⁻¹ after 40 hours of operation.     

Development of Al2O3/glass-based multi-layer composite seals for planar intermediate-temperature solid oxide fuel cells

In this paper, the novel multi-layer composite seals for planar solid oxide fuel cells are studied. The composite seals with sandwiched structure include Al₂O₃-based tape as support and glass-ceramic slurry as binder connecting the interface of the neighboring components. The result finds out that glass-ceramic slurry with 20 wt% Al₂O₃ has the suitable strength and deformability. The thermal cycle characteristics are greatly improved by using the multi-layer composite seals, and the corresponding leakage rates are lower than 0.025 sccm cm⁻¹ for 20 thermal cycles at the inlet pressure ranging from 0.5 psi to 2 psi. SEM investigations show a very compact and good adhesion between the neighboring components, which can minimize the leakage paths. Single cell testing is used to examine the performance of the seals. The value of open circuit voltage is 1.17 V. At the constant discharge current density of 0.37 A cm⁻², the voltage is stabilized at about 0.85 V for 50 h. The results demonstrate that the novel multi-layer composite seals are good candidate for SOFC application.     

Evaluation of the thermal and structural stability of planar anode-supported solid oxide fuel cells using a 10 × 10 cm2 single-cell test

The present work investigated the thermal and structural stability of planar anode-supported solid oxide fuel cells (SOFCs) using a 10 × 10 cm² single-cell test. First, the gasket study was performed in which the sealing efficiency and hydrodynamics were examined to obtain the control parameters for sealing design. Two types of high-temperature gaskets were evaluated for application in the SOFC test, both with sealing efficiencies over 99.99%; both of them did not ensure the gas tightness perfectly, and we selected the fuel cell material gasket due to a lower leak factor than the Magnex gasket at whole inlet flow rates. After this gasket sealing test, the thermal and structural stability of a planar anode-supported SOFC was evaluated by changing temperature repeatedly between room temperature and 850 °C. For the first high flow test, the open circuit voltage (OCV) agreed with the theoretical value, and the voltage decreased linearly as the current density increased. In addition, the measured temperature distribution had a similar trend compared with the previous numerical analysis during the first reduction condition. However, after lowering the temperature and raising it again, the OCV during the second low flow test decreased and fuel crossover loss occurred; additionally, the voltage decreased irregularly as the current density increased. After completing the tests and dissembling the single cell specimen, the cracked mark was placed in the center of the cell like the calculated and measured results. From the dispersed oxygen contents in the anode using scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy, we concluded that the crack was induced by the reduction and oxidation (RedOx) cycle instability from even a small leakage through the gasket. Finally, we found that the planar SOFC was vulnerable to the thermal RedOx cycle induced by non-perfect sealing, and it was confirmed that the requirement of the gas tightness should be fulfilled in order to obtain the longer life and the higher stability for the solid oxide fuel cell.     

Effect of operating temperature on creep and damage in the bonded compliant seal of planar solid oxide fuel cell

This paper studies the effect of operating temperature on creep and damage in bonded compliant seal of solid oxide fuel cell by finite element method. A strain based creep damage model is used, and its feasibility to predict the creep damage behavior of the materials is verified firstly by the experimental data. The results show that the failure locates at the foil and the location varies with the temperature increasing. When the temperature is lower than 600 °C, there is nearly no crack occurs. When the temperature is 600 °C, the creep crack belongs to internal crack and the length is about 2.5 mm. While the temperature is 650 °C or higher, the crack locates at the foil surface and the length is larger than 25 mm at an operation time of 50,000 h. Compared to the size of the whole structure, an internal crack of 2.5 mm is small and the gas leakage will not happen. Therefore, it can satisfy the requirement of safe operation for more than 40,000 h. Thus, it recommends that the operating temperature should not be higher than 600 °C on the condition of insuring the power performance and operation cost of the SOFC.     

A solid state thermogalvanic cell harvesting low-grade thermal energy

A high performance polymer electrolyte thermogalvanic cell, which converts thermal energy to electrical energy directly, is transformed from a proton exchange membrane fuel cell. The transform is realized by connecting the anode and cathode chamber with a gas tube and filling hydrogen to both chambers. Provided a heat flux through the cell, hydrogen is consumed in the cold side and regenerated in the hot side while circulating in two chambers during operation. The Seebeck coefficient is 0.531 mV K^?1 at a cold side temperature of 60.0 °C and the maximum power density could reach up to 20 μW cm^?2 with a temperature difference of 15.3 °C between two electrodes.     

Electrochemical properties and durability of in-situ composite cathodes with SmBa0.5Sr0.5Co2O5+δ for metal supported solid oxide fuel cells

The electrochemical properties and long-term performance of an in-situ composite cathode comprised of SmBa_0.5Sr_0.5Co₂O_5+δ (SBSCO) and Ce_0.9Gd_0.1O_2?δ (CGO91) are investigated for metal supported solid oxide fuel cell (MS-SOFC) application.The Area Specific Resistance (ASR) of an in-situ composite cathode comprised of 50 wt% of SBSCO and 50 wt% of CGO91 (SBSCO:50) is 0.031 Ω cm² in the first stage of measurement at 700 °C; this value of ASR increases to 0.138 Ω cm² after 1000 h. The ASR of SBSCO:50 (in-situ sample at 750 °C) is 0.014 Ω cm² at the initial stage of measurement; the increase of ASR after 1000 h at 750 °C is only 0.067 Ω cm². These results suggest that the optimum temperature for in-situ firing of an SBSCO:50 cathode sample of MS-SOFC is higher than 700 °C, ideally around 750 °C.     

Performance and durability of an anode-supported solid oxide fuel cell with a PdO/ZrO2 engineered (La0.8Sr0.2)0.95MnO3-δ-(Y2O3)0.08(ZrO2)0.92 composite cathode

PdO/ZrO₂ co-infiltrated (La_0.8Sr_0.2)_0.95MnO_3-δ-(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM-YSZ) composite cathode (PdO/ZrO₂+LSM-YSZ), which adsorbs more oxygen than equal amount of PdO/ZrO₂ and LSM-YSZ, is developed and used in Ni-YSZ anode-supported cells with YSZ electrolyte. The cells are investigated firstly at temperatures between 650 and 750 °C with H₂ as the fuel and air as the oxidant and then polarized at 750 °C under 400 mA cm^?2 for up to 235 h. The initial peak power density of the cell is in the range of 438–1207 mW cm^?2 at temperatures from 650 to 750 °C, corresponding to polarization resistance from 1.04 to 0.35 Ω cm². This result demonstrates a significant performance improvement over the cells with other kinds of LSM based cathode. The cell voltage at 750 °C under 400 mA cm^?2 decreases from initial 0.951 to 0.89 V after 170 h of current polarization and remains essentially stable to the end of current polarization. It is identified that the self-limited growth of PdO particles is responsible for the cell voltage decrease by reducing the length of triple phase boundary affecting the high frequency steps involved in oxygen reduction reaction in the cathode.     

Electrochemical performance of different carbon fuels on a hybrid direct carbon fuel cell

In this work, three processed carbon fuels including activated carbon, carbon black and graphite have been employed to investigate influence of the chemical and physical properties of carbon on the HDCFC performance in different anode atmospheres at 650–800 °C. The results reveal that the electrochemical activity is strongly dependent on crystalline structure, thermal stability and textural properties of carbon fuels. The activated carbon samples demonstrate a better performance with a peak power density of 326 mW cm^?2 in CO₂ at 750 °C, compared to 147 and 59 mW cm^?2 with carbon black and graphite samples, respectively. Compared to the ohmic resistance, the polarization resistance plays a more dominated role in the cell performance. When replacing N₂ by CO₂ purge gas, the power density is the strongly temperature dependent due to the Boudouard reaction.     

High performance BaFe1−xBixO3−δ as cobalt-free cathodes for intermediate temperature solid oxide fuel cells

Bi₂O₃ doped BaFeO_3?δ on the B-site as a cobalt free perovskite cathode for intermediate temperature solid oxide fuel cells is evaluated. The BaFe_1?xBi_xO_3?δ (BFBx) powders are synthesized by solid state reaction. It is found that Bi₂O₃ doping stabilizes the BaFeO₃ cubic phase. The new cathode is compatible with Gd_0.1Ce_0.9O_1.95 even calcined at 1000 °C for 10 h. The electronic conductivity shows a transformation from semiconductor to metal conductor, and achieves its maximum value of 28.1 S cm^?1 for BFB10 at 800 °C. The δ is as high as 0.408 for BFB10 determined by iodometric titration. This leads to the free volume in crystal lattice of BFB10 21.60% higher than that of BaNb_0.05Fe_0.95O_3?δ. The area specific resistance is only 0.133 Ω cm² for BFB10 at 750 °C and the average TEC is 26.697 × 10^?6 K^?1 measured from room temperature to 800 °C. The peak power density of Ni-YSZ|YSZ|GDC|BFB10 cell is 646.28 mW cm^?2 at 750 °C, higher than that of single cell using LSCF as cathode. These show that BFBx perovskite oxides with cubic phase are promising cathodes for intermediate temperature solid oxide fuel cells.     

Enhanced ionic conductivity of yttria-stabilized ZrO2 with natural CuFe-oxide mineral heterogeneous composite for low temperature solid oxide fuel cells

We report for the first time that the commercial yttrium stabilized zirconia (YSZ) nanocomposite with a natural CuFe-oxide mineral (CF) exhibits a greatly enhanced ionic conductivity in the low temperature range (500–600 °C), e.g. 0.48 S/cm at 550 °C. The CF–YSZ composite was prepared via a nanocomposite approach. Fuel cells were fabricated by using a CF–YSZ electrolyte layer between the symmetric electrodes of the Ni_0.8Co_0.2Al_0.5Li (NCAL) coated Ni foam. The maximum power output of 562 mW/cm² has been achieved at 550 °C. Even the CF alone to replace the electrolyte the device reached the maximum power of 281 mW/cm² at the same temperature. Different ion-conduction mechanisms for YSZ and CF–YSZ are proposed. This work provides a new approach to develop natural mineral composites for advanced low temperature solid oxide fuel cells with a great marketability.     

A pressurized ammonia-fed planar anode-supported solid oxide fuel cell at 1–5 atm and 750–850°C and its loaded short stability test

Ammonia is a useful energy carrier for solid oxide fuel cell (SOFC) with advantages over hydrogen. Understanding of the performance and stability of ammonia-fed SOFC operated at elevated pressure (p) is an important step towards the development of high-efficiency hybrid SOFC power system with micro gas turbine (MGT). This paper reports cell performance, electrochemical impedance spectra (EIS), and stability measurements of a pressurized ammonia-fed anode-supported SOFC at p = 1–5 atm and T = 750–850°C using a planar (50 × 50 mm²) single-full-cell (400 μm Ni-YSZ anode/3 μm YSZ electrolyte/12 μm LSC-GDC cathode). The full cell together with metallic frames and current collectors are sandwiched by a pair of rib-channel flow distributors (interconnectors) in a high-pressure testing facility. Results show that pressurization and increasing temperature enhance the ammonia-fed SOFC performance significantly having almost the same power densities as those of hydrogen/nitrogen-fed SOFC, as substantiated and explained by EIS data and an equivalence circuit model where the effects of p and T on ohmic, gas diffusion, and gas conversion impedances are shown. Moreover, the loaded short (10 h) stability tests at 700°C and 0.8 V for 1 atm/3 atm cases reveal no/little power degradation, where the microstructures without any crack within the scale of SEM observation and nearly the same element atomic percentages of Ni-YSZ anode surfaces from EDX spectra are found. These results suggest that the pressurized ammonia-fed SOFC is a promising candidate for the hybrid SOFC-MGT power generation.